"Hydridic Hydrogen-Bond Donors" Are Not Hydrogen-Bond Donors.

Herein, we dismiss a recent proposal by Civiš, Hobza, and co-workers to modify the IUPAC definition of hydrogen bonds in order to expand the scope from protonic Y-H to hydridic Y-H hydrogen-bond donor fragments [ , , 8550]. Based on accurate Kohn-Sham molecular orbital (KS-MO) analyses, we falsify the conclusion that interactions involving protonic and hydridic hydrogens are both hydrogen bonds; they are not. Instead, our quantitative KS-MO, energy decomposition, and Voronoi deformation density analyses reveal two fundamentally different bonding mechanisms for protonic Y-H and hydridic Y-H fragments which go with charge transfer in opposite directions.

The nature of metallophilic interactions in closed-shell d-d metal complexes.

We have quantum chemically analyzed the closed-shell d-d metallophilic interaction in dimers of square planar [M(CO)X] complexes (M = Ni, Pd, Pt; X = Cl, Br, I) using dispersion-corrected density functional theory at ZORA-BLYP-D3(BJ)/TZ2P level of theory. Our purpose is to reveal the nature of the [X(CO)M]⋯[M(CO)X] bonding mechanism by analyzing trends upon variations in M and X. Our analyses reveal that the formation of the [M(CO)X] dimers is favored by an increasingly stabilizing electrostatic interaction when the M increases in size and by more stabilizing dispersion interactions promoted by the larger X.

Blueshift in Trifurcated Hydrogen Bonds: A Tradeoff between Tetrel Bonding and Steric Repulsion.

The front cover artwork is provided by the TheoCheM group at the Vrije Universiteit Amsterdam. The image shows how, in X •••H C-Y complexes, the Lewis base X tetrel-binds to the central C while sterically pushing the H atoms towards C; hence, the compression and blueshift of the H-C bonds. Read the full text of the Research Article at 10.

Multiple hydrogen-bonded dimers: are only the frontier atoms relevant?

Non-frontier atom exchanges in hydrogen-bonded aromatic dimers can induce significant interaction energy changes (up to 6.5 kcal mol). Our quantum-chemical analyses reveal that the relative hydrogen-bond strengths of -edited guanine-cytosine base pair isosteres, which cannot be explained from the frontier atoms, follow from the charge accumulation in the monomers.

Blueshift in Trifurcated Hydrogen Bonds: A Tradeoff between Tetrel Bonding and Steric Repulsion.

We have quantum chemically investigated the origin of the atypical blueshift of the H-C bond stretching frequency in the hydrogen-bonded complex X •••H C-Y (X, Y=F, Cl, Br, I), as compared to the corresponding redshift occurring in Cl •••H N and Cl •••H C-H, using relativistic density functional theory (DFT) at ZORA-BLYP-D3(BJ)/QZ4P. Previously, this blueshift was attributed, among others, to the contraction of the H-C bonds as the H C moiety becomes less pyramidal. Herein, we provide quantitative evidence that, instead, the blueshift arises from a direct and strong X •••C interaction of the HOMO of A with the backside lobe on carbon of the low-lying C-Y antibonding σ* LUMO of the H C-Y fragment.

Intermolecular Covalent Interactions: Nature and Directionality.

Quantum chemical methods were employed to analyze the nature and the origin of the directionality of pnictogen (PnB), chalcogen (ChB), and halogen bonds (XB) in archetypal F Z⋅⋅⋅F complexes (Z=Pn, Ch, X), using relativistic density functional theory (DFT) at ZORA-M06/QZ4P. Quantitative Kohn-Sham MO and energy decomposition analyses (EDA) show that all these intermolecular interactions have in common that covalence, that is, HOMO-LUMO interactions, provide a crucial contribution to the bond energy, besides electrostatic attraction. Strikingly, all these bonds are directional (i.

Iodine Gauche Effect Induced by an Intramolecular Hydrogen Bond.

The conformer in 1-X,2-Y-disubstituted ethanes, that is, the staggered orientation in which X and Y are in closer contact, is only favored for relatively small substituents that do not give rise to large X···Y steric repulsion. For more diffuse substituents, weakly attractive orbital interactions between antiperiplanar bonds (i.e.

Cleaner and stronger: how 8-quinolinolate facilitates formation of Co(III)-thiolate from Co(II)-disulfide complexes.

The formation of Co(III)-thiolate complexes from Co(II)-disulfide complexes using the anionic ligand 8-quinolinolate (quin) has been studied experimentally and quantum chemically. Two Co(II)-disulfide complexes [Co(LSSL)(Cl)] ( = 1 or 2; LSSL = 2,2'-disulfanediylbis(,-bis(pyridin-2-ylmethyl)ethan-1-amine; LSSL = 2,2'-disulfanedylbis (-((6-methylpyridin-2-yl)methyl)--(pyridin-2-ylmethyl) ethan-1-amine) have been successfully converted with high yield to their corresponding Co(III)-thiolate complexes upon addition of the ligand 8-quinolinolate. Using density functional theory (DFT) computations the d-orbital splitting energies of the cobalt-thiolate compounds [Co(LS)(quin)] and [Co(LS)(quin)] were estimated to be 3.

Probing the redox-conversion of Co(II)-disulfide to Co(III)-thiolate complexes: the effect of ligand-field strength.

The redox-conversion reaction of cobalt(II)-disulfide to cobalt(III)-thiolate complexes triggered by addition of the bidentate ligand 2,2'-bipyridine has been investigated. Reaction of the cobalt(II)-disulfide complex [Co(LSSL)(X)] (LSSL = di-2-(bis(2-pyridylmethyl)amino)-ethyldisulfide; X = Cl or Br) [1X] with 2,2'-bipyridine (bpy) resulted in the formation of two different products, namely the cobalt(III)-thiolate complex [Co(LS)(bpy)]X and the unexpected side product [Co(LSSL)(bpy)(X)]X. Crystals of [Co(LSSL)(bpy)(Cl)](BPh) [2Cl](BPh) obtained after anion exchange showed the cobalt(II) ions to be in octahedral geometries with the nitrogen donors of the disulfide ligand arranged in a facial conformation and the chloride ion to the tertiary amine nitrogen.

σ-Electrons Responsible for Cooperativity and Ring Equalization in Hydrogen-Bonded Supramolecular Polymers.

Invited for this month's cover are collaborators from the TheoCheM group of the Vrije Universiteit Amsterdam and the University of Perugia. The cover picture shows a σ-electron traveling through a hydrogen-bonded squaramide linear chain. The charge transfer within the σ-electronic system is the cause for the cooperativity in the investigated urea, deltamide, and squaramide polymers.

σ-Electrons Responsible for Cooperativity and Ring Equalization in Hydrogen-Bonded Supramolecular Polymers.

We have quantum chemically analyzed the cooperative effects and structural deformations of hydrogen-bonded urea, deltamide, and squaramide linear chains using dispersion-corrected density functional theory at BLYP-D3(BJ)/TZ2P level of theory. Our purpose is twofold: (i) reveal the bonding mechanism of the studied systems that lead to their self-assembly in linear chains; and (ii) rationalize the C-C bond equalization in the ring moieties of deltamide and squaramide upon polymerization. Our energy decomposition and Kohn-Sham molecular orbital analyses reveal cooperativity in all studied systems, stemming from the charge separation within the σ-electronic system by charge transfer from the carbonyl oxygen lone pair donor orbital of one monomer towards the σ* N-H antibonding acceptor orbital of the neighboring monomer.

Dipolar repulsion in α-halocarbonyl compounds revisited.

The concept of dipolar repulsion has been widely used to explain several phenomena in organic chemistry, including the conformational preferences of carbonyl compounds. This model, in which atoms and bonds are viewed as point charges and dipole moment vectors, respectively, is however oversimplified. To provide a causal model rooted in quantitative molecular orbital theory, we have analyzed the rotational isomerism of haloacetaldehydes OHC-CHX (X = F, Cl, Br, I), using relativistic density functional theory.

The pnictogen bond: a quantitative molecular orbital picture.

We have analyzed the structure and stability of archetypal pnictogen-bonded model complexes D3PnA- (Pn = N, P, As, Sb; D, A = F, Cl, Br) using state-of-the-art relativistic density functional calculations at the ZORA-M06/QZ4P level. We have accomplished two tasks: (i) to compute accurate trends in pnictogen-bond strength based on a set of consistent data; and (ii) to rationalize these trends in terms of detailed analyses of the bonding mechanism based on quantitative Kohn-Sham molecular orbital (KS-MO) theory in combination with a canonical energy decomposition analysis (EDA) and Voronoi deformation density (VDD) analyses of the charge distribution. We have found that pnictogen bonds have a significant covalent character stemming from strong HOMO-LUMO interactions between the lone pair of A- and σ* of D3Pn.

A Quantitative Molecular Orbital Perspective of the Chalcogen Bond.

Invited for this month's cover are the groups of Prof. Dr. Teodorico C.

A Quantitative Molecular Orbital Perspective of the Chalcogen Bond.

We have quantum chemically analyzed the structure and stability of archetypal chalcogen-bonded model complexes D Ch⋅⋅⋅A (Ch = O, S, Se, Te; D, A = F, Cl, Br) using relativistic density functional theory at ZORA-M06/QZ4P. Our purpose is twofold: (i) to compute accurate trends in chalcogen-bond strength based on a set of consistent data; and (ii) to rationalize these trends in terms of detailed analyses of the bonding mechanism based on quantitative Kohn-Sham molecular orbital (KS-MO) theory in combination with a canonical energy decomposition analysis (EDA). At odds with the commonly accepted view of chalcogen bonding as a predominantly electrostatic phenomenon, we find that chalcogen bonds, just as hydrogen and halogen bonds, have a significant covalent character stemming from strong HOMO-LUMO interactions.

The Gauche Effect in XCH CH X Revisited.

We have quantum chemically investigated the rotational isomerism of 1,2-dihaloethanes XCH CH X (X = F, Cl, Br, I) at ZORA-BP86-D3(BJ)/QZ4P. Our Kohn-Sham molecular orbital (KS-MO) analyses reveal that hyperconjugative orbital interactions favor the gauche conformation in all cases (X = F-I), not only for X = F as in the current model of this so-called gauche effect. We show that, instead, it is the interplay of hyperconjugation with Pauli repulsion between lone-pair-type orbitals on the halogen substituents that constitutes the causal mechanism for the gauche effect.

Chalcogen bonds: Hierarchical ab initio benchmark and density functional theory performance study.

We have performed a hierarchical ab initio benchmark and DFT performance study of D Ch•••A chalcogen bonds (Ch = S, Se; D, A = F, Cl). The ab initio benchmark study is based on a series of ZORA-relativistic quantum chemical methods [HF, MP2, CCSD, CCSD(T)], and all-electron relativistically contracted variants of Karlsruhe basis sets (ZORA-def2-SVP, ZORA-def2-TZVPP, ZORA-def2-QZVPP) with and without diffuse functions. The highest-level ZORA-CCSD(T)/ma-ZORA-def2-QZVPP counterpoise-corrected complexation energies (ΔE ) are converged within 1.

Nature and Strength of Lewis Acid/Base Interaction in Boron and Nitrogen Trihalides.

We have quantum chemically investigated the bonding between archetypical Lewis acids and bases. Our state-of-the-art computations on the X B-NY Lewis pairs have revealed the origin behind the systematic increase in B-N bond strength as X and Y are varied from F to Cl, Br, I, H. For H B-NY , the bonding trend is driven by the commonly accepted mechanism of donor-acceptor [HOMO(base)-LUMO(acid)] interaction.

Halogen Bonds in Ligand-Protein Systems: Molecular Orbital Theory for Drug Design.

Halogen bonds are highly important in medicinal chemistry as halogenation of drugs, generally, improves both selectivity and efficacy toward protein active sites. However, accurate modeling of halogen bond interactions remains a challenge, since a thorough theoretical investigation of the bonding mechanism, focusing on the realistic complexity of drug-receptor systems, is lacking. Our systematic quantum-chemical study on ligand/peptide-like systems reveals that halogen bonding is driven by the same bonding interactions as hydrogen bonding.

Could Quantum Mechanical Properties Be Reflected on Classical Molecular Dynamics? The Case of Halogenated Organic Compounds of Biological Interest.

Essential to understanding life, the biomolecular phenomena have been an important subject in science, therefore a necessary path to be covered to make progress in human knowledge. To fully comprehend these processes, the non-covalent interactions are the key. In this review, we discuss how specific protein-ligand interactions can be efficiently described by low computational cost methods, such as Molecular Mechanics (MM).

Molecularly imprinted polymers for selective adsorption of quinoline: theoretical and experimental studies.

The effects of solvent on the synthesis of molecularly imprinted polymers (MIPs) for the selective adsorption of quinoline were evaluated in this work. The MIPs were synthesized by the "bulk" method using the quinoline molecule (IQ) as a template in different solvents, such as toluene (MIPT) and chloroform (MIPC). The adsorbents were characterized by thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), and N adsorption/desorption measurements.